1. Field of the Invention
This invention relates to a structure for coupling a back cover with a case band in wrist watches, and more particularly to an improvement of a structure for coupling a back cover with a case band in acoustic wrist watches of strange appearance.
2. Description of the Prior Art
In order to couple a back cover with a case band in acoustic wrist watches, various structures therefor have heretofore been proposed. In such type of acoustic wrist watch in which sound is created by vibrating a vibrating plate to which piezo-electric element is attached by means of piezo-electric effect, it is requested to maintain a wide effective area for the vibrating plate as much as possible in order to obtain a sufficient sound volume, so that the vibrating plate is generally provided on the bottom portion of the watch case. Accordingly such type of the wrist watch as mentioned above comes to a thick structure as a whole in the case when the back cover is coupled with the case band, and such wrist watch cannot satisfy recent requests for thinning, lightening, saving resources, and reducing cost of wrist watches. More specifically, a conventional structure is such that, as shown in FIG. 1, a stepped portion 1a is provided on the inner wall in the interior of an attaching portion for band of a case band 1, a vibrating plate 3 is supported on the stepped portion 1a through an O-ring 2 by an end portion of a back cover 4 on a part of which an acoustic sound hole 4a is bored and at the same time, the vibrating plate 3 is fitted to and engaged with the case band 1 by means of chamferring, so that a thick material must be subjected to machining and stamping because of a coupling structure of the back cover 4 with the case band 1, and therefore the conventional structure has a disadvantage of inferior workability. Furthermore a highly skilled working technique is required in the case where a fitting portion consisting of the back cover and the case band in a wrist watch has a strange profile and the back cover and the case band are chamferred in a prescribed fitting condition.